Heat-resistant nickel-base sheet alloy



May 28, 1957 l. s. SERVI ETAL 2,793,950

HEAT-RESISTANT NICKELBASE SHEET ALLOY Filed July 3, 1955 a n m On n u 30 n 3 In a. on H l m cm n0 5 Q. on om 00. ccm v 3m aunldna sanou semi R.SPEN ELOW,JR. 9.

INVENTOR ITALO 8 ATTORNEY United States Patent HEAT-RESISTANTNICKEL-BASE SHEET ALLOY Italo S. Servi, Niagara Falls, and Howard R.Spendelow, Jr., Snyder, N. Y., assignors to Union Carbide and CarbonCorporation, a corporation of New York Application July a, 1953, SerialNo. 365,854

8 Claims. (Cl. 75-171 This invention relates to heat-resistantboron-free, nickel-base alloys capable of being rolled into sheet. Morespecifically, this invention relates to such nickelbase alloys havinghigh stress-rupture properties and articles made therefrom.

The increasing demand in the aeronautical fields for alloys havingstress-resistance at high temperatures, particularly in jet enginedesign, is constantly paced by the restrictions of the so-calledstrategic metals. As jet engines develop, they tend to feed more andmore upon the metals that are less and less available, columbium,tantalum, tungsten, cobalt being the metals currently in use. It wouldbe greatly desirable to have available an alloy of the requiredproperties for such use, but that utilizes a minimum, or none, of thesestrategic metals.

It is the object of this invention to provide a heatresistant alloy,comprising a boron-free, nickel-base alloy containing chromium, iron,molybdenum, titanium, aluminum and carbon, that can be hot-worked intosheet, bars and articles that have high stress-rupture properties.

The alloy of the invention is boron-free and has the composition 14% to17% chromium, 8% to 12% iron, 4% to 7% molybdenum, 2.25% to 5.0%titanium, 1.75% to 2.50% aluminum, 0.08% to 0.25% carbon, remaindernickel and incidental impurities. A preferred composition is within thefollowing limits: 14% to 16% chromium, 8% to 12% iron, to 6% molybdenum,2.25% to 4% titanium, 1.75% to 2.25% aluminum, 0.12% to 0.16% carbon,remainder nickel and incidental impurities.

In the accompanying drawings:

Fig. 1 is a curve graphically illustrating the effect of the ironcontent on the stress-rupture life of the alloys of the invention; and

Fig. 2 is a curve graphically illustrating the effect of the molybdenumcontent on the stress-rupture life of the alloys of the invention.

The alloy of the invention is closely balanced and the ranges listed arecritical. The desirable properties of the alloy of the invention arisefrom close balancing, the balancing representing a compromise betweenhigh stress-rupture properties and the ability of being rolled intosheet. The inter-relationship of the alloying elements to each other, inthe ranges set forth, gives rise to the distinguishing characteristicsof the alloy. For example, not only are the proportions of the elementschromium, molybdenum and iron present in the alloy of the inventionindividually critical to the attainment of the desired properties, butthey are critically interrelated with respect to each other.

The accompanying drawings serve to illustrate clearly the criticality ofthe ranges of the alloying elements.

Fig. 1 is a graphic representation of stress-rupture life of the alloyof the invention at 1600" F. using 20,000 pounds per square inch. Theiron content was varied, as shown in the graph, in an alloy having thecomposition: 15% to 16% chromium, about 5.5% molybdenum, 1.80% to 2.25%aluminum, 2.50% to 2.75% titanium, 0.12% to 0.15% carbon, balance nickeland incidental impurities. An examination of the graph points out theclose balancing and criticality of the iron content in the alloy of theinvention. The maximum stress-rupture life of about 400 hours is reachedin a narrow range of iron, a reduction in iron content to below thisrange serves to reduce the stress-rupture life sharply, for example, thestress-rupture life is shortened by about one-fourth for one hundredhours, if the iron content is reduced to about 6%. The significance ofthe close balancing and criticality is even more sharply noted if theiron content is increased beyond its narrow range, for example, thestress-rupture life is shortened by about onehalf, or two hundred hours,if the iron content is increased about 6% beyond its narrow range.

Further pointing out the criticality of the ranges of the alloyingelements, Fig. 2 is a graphic representation of stressrupture life ofthe alloy of the invention at 1500 F. using 35,000 pounds per squareinch. The molybdenum content was varied, as shown in the graph, in analloy having the composition: 15% to 16% chromium, about 8.5% iron,1.75% to 2.25% aluminum, 2.50% to 2.75% titanium, 0.11% to 0.16% carbon,balance nickel and incidental impurities. An examination of the graphpoints out the close balancing and criticality of the molybdenum contentin the alloy of the invention, it is to be noted, to an even closerdegree than that of the iron content. The maximum stressrupture life ofabout hours is reached in an extremely narrow range of molybdenum, areduction in molybdenum content to below this range serves to reduce thestress-rupture life with remarkable sharpness, for example, thestress-rupture life is shortened by greater than two-thirds, or aboutone hundred and twenty-five hours, if the molybdenum content is reducedby about 3%. The significance of the close balancing and criticality isalso sharply noted if the molybdenum content is increased beyond itsnarrow range, for example, the stress-rupture life is shortened by aboutone-half, or ninety hours, if the molybdenum content is increased about3%.

To recapitulate, in view of the accompanying graphs, the significance ofthe careful adjustment of the proportions of the alloying elements inthe alloy of the invention and their narrowly restricted amounts areseen to be of paramount importance in achieving the physical propertiesthat give to the alloy of the invention its distinguishingcharacteristics.

The amounts of aluminum and titanium in the alloy of the invention areno less critical than the other elements. An increase in aluminum andtitanium is beneficial to the strength of the alloy of the invention butimpairs the hot-workability and cold-formability. Moreover, the ratio oftitanium to aluminum is of particular importance; not only are thepercentages listed for each of extreme importance, but their proportionto each other is also of great importance. In any given composition theamount of titanium is always in excess of the amount of aluminum, beingpresent in a proportion to each other. A preferred ratio is about l-l /zparts titanium to 1 part aluminum.

Among the distinguishing properties of the alloy is the constancy ofyield strength from room temperature to expected operating temperatures.The sharp break of other comparable alloys in yield strength serves topoint out one of the distinctive advantages of the alloy of theinvention. Other distinguishing properties of the alloy of the inventionare its hotworkability, room-temperature ductility and high temperaturestrength. Such properties permit the fabrication by hot working ofsheet, bar stock, forgings, plates and articles for service at elevatedtemperatures under stress. Another desirable property of the alloy ofthe invention that sets it apart from other comparable alloys is that noartificial aging treatment is necesary to develop stressruptureproperties superior to properties of comparable current alloys.

Preferably, the alloys of the invention are melted and cast in vacuo, ashereinafter set forth in detail, regardless of the amount of thealloying metals within their stated ranges. Vacuum melting and castingconsistently produce sound ingots that can be rolled Without difiiculty.However, if the titanium content is on the low side of the range listed,the alloy may be produced by melting in air in the conventional mannerwith certain requirements such as casting in a sand mold as set forthhereinafter. If the titanium content exceeds about 2 /2% to 3%, vacuummelting and casting must be employed.

When the vacuum melting technique is used, a preferred method is tocharge all material into the furnace using an excess of carbon. Thefurnace is partially evacuated and the charge is melted. When the chargeis molten, the power is reduced to an amount sufficient to maintain thecharge in a molten state and the pressure reduced slowly, exercisingcare to prevent a violent boil, during which time the excess carbon isreacting with the impurities in the charge. (The reaction can beretarded by increasing the chamber pressure with argon.) The pressuresshould finally be reduced to about 0.3 mm. to 0.5 mm. and thentemperature and pressure are held constant until apparent reactionceases, after which the heat is poured in a partial atmosphere of argon.

When the air-melting technique is used, the alloy is melted inconventional manner in air exercising the usual precautions. Whenmelted, the alloy is cast into a sand mold provided with a hot top. Anexothermic hot-topping compound, for example, that commerciallyavailable under designation Thermotomic No. 2, manufactured byPittsburgh Metals Purifying Co., Pittsburgh, Pa., should be placed inthe hot top. By exercising these precautions, a sound ingotsubstantially free of objectionable inclusions is produced. Clean, soundingots of 6 x 6 x 40 inches have been successfully made by this method.

After casting of the alloy of the invention by either method above setforth, the alloy is hot-worked in a temperature range of 1050 C. to 1180C.

The following data show the excellent physical properties of specificexamples of the alloy of the invention. Heat No. A was prepared by theair-melting technique before set forth, and beat No. B was prepared bythe vacuum melting technique before set forth. Attention is directed tothe exceptional rupture life of 167.7 hours at 1800" F. with a load of10,000 pounds per square inch for heat B, demonstrating one of thedistinguishing characteristics of the alloy of the invention.

Heat N A B Composition:

Percent Chromium.. Percent Iron Percent lilolybdenum. Percent TitaniumPercent Aluminurm. Percent Carboiu.

.. Pr t r-s e Autographic stress strain: 0.109-inch hot-rolled,mill-annealed I sheet Stress rupture data: 0.25-inch hot-rolledmill-annealed round.

Heat No. B

Rupture Elonga Lift, tion, Hr Percent.

151. 8 l0. 2 226. 8 7. 4 285. 1 14. it 338. 0 14. 9 107. 7 35. 8

l Mill-annealed-heated at 2150 F. and air-cooled.

The outstanding properties of the alloy of the invention recommend itsuse for fabrication by hot-working by rolling into sheet material or byother means of severe hot-working to form turbine buckets, tail conesfor jet aircraft, valves or parts thereof, or the like; in short, formetal or metal articles for use at high temperatures under stress.

What is claimed is:

l. A boron-free, nickel-base alloy capable of being rolled into sheetconsisting essentially of 15% to 17% chromium, 8% to 12% iron, 4% tomolybdenum, titanium and aluminum in a ratio of about 1 /1 partstitanium to 1 part aluminum, the titanium being present in a range from2.25% to 5.0%, 0.08% to 0.25% carbon, remainder nickel and incidentalimpurities.

2. A boron-free, nickel-base alloy capable of being rolled into sheetconsisting essentially of 14% to 16% chromium, 8% to 12% iron, 5% to 6%molybdenum, 2.25% to 4% titanium, 1.75% to 2.25% aluminum, 0.12% to0.16% carbon, remainder nickel and incidental impurities.

3. A boron-free, nickel-base alloy capable of being rolled into sheetconsisting essentially of 14% to 17% chromium, 8% to 12% iron, 4% to 7%molybdenum. 2.25% to 5.0% titanium, 1.75% to 2.50% aluminum, up to 2.5%cobalt, 0.08% to 0.25% carbon, remainder nickel and incidentalimpurities, the ratio of titanium to aluminum being between 1.0 to 1 and1.5 to l.

4. A heat-resistant, hot-workable boron-free, nickelbase alloy, capableof being fabricatzd into bar stock, consisting essentially of 14% to 17%chromium. 8% to 12% iron, 4% to 7% molybdenum, 2.25% to 5.0% titanium,0.08% to 0.25% carbon, remainder aluminum, nickel and incidentalimpurities, the ratio of titanium to aluminum being between 1.0 to l and1.5 to 1.

5. Boron-free, nickel-base article having essentially the composition14% to 17% chromium, 8% to 12% iron, 4% to 7% molybdenum. 2.25% to 5.0%titanium. 1.75% to 2.5 0% aluminum, 0.08% to 0.25% carbon. balancenickel and incidental impurities, the ratio of titanium to aluminumbeing between 1.0 to 1 and 1.5 to l.

6. A nickel-base alloy exhibiting high strength characteristics andhot-workability and cold formability properties, in the absence of borontherein, said alloy consisting essentially of 14% to 17% chromium, 8% to12% iron, 4% to 7% molybdenum, 1.75% to 2.50% aluminum, 0.08% to 0.25%carbon, remainder titanium, nickel and incidental impurities, the ratioof titanium to aluminum being between 1.0 to 1 and 1.5 to 1.

7. In the art of manufacturing nickel-base alloy for high temperatureuse of the type normally containing boron, chromium, molybdenum andiron, the method of imparting hot workability and cold formability properties, which comprises incorporating titanium and aluminum in saidalloy, regulating the ratio of said titanium to said aluminum between1.0 to 1 and 1.5 to 1. excluding the embodiment of boron therein whilerestricting the alloy composition to 14% to 17% chromium. 8% to 12%iron, 4% to 7% molybdenum. 2.25% to 5.0% titanium, 1.75% to 2.50%aluminum, 0.08% to 0.25 carbon, remainder nickel and incidentalimpurities.

8. A nickel-base alloy characterized by high tempera ture strength andby hot workability and cold formabil ty consisting of 14% to 17%chromium, 2.25% to 5.0% titanium, 1.75% to 2.50% aluminum, 0.08% to0.25% carbon and the remainder nickel, molybdenum, iron and incidentalimpurities, said molybdenum and iron being critically balanced inamounts between 4% and 7% and between 8% and 12%, respectively, forimparting peak rupture life without afiecting the workability andformability of said alloy, the ratio of titanium to aluminum beingbetween 1.0 to 1 and 1.5 to 1.

Franks et a1. Dec. 16, 1947 Bieber et a1. July 18, 1950 FOREIGN PATENTSAustralia Dec. 17, 1941 Australia Oct. 26, 1949

2. A BORON-FREE, NICKLE-BASE ALLOY CAPABLE OF BEING ROLLED INTO SHEETCONSISTING ESSENTIALLY OF 14% TO 16% CHROMIUM, 8% TO 12% IRON 5% TO 6%MOLYBDENUM, 2.25% TO 4% TITANIUM, 1.75% TO 2.25% ALUMINUM, 0.12% TO0.16% CARBON, REMAINDER NICKLE AND INCIDENTAL IMPURITIES.
 7. IN THE ARTOF MANUFACTURING NICKLE-BASE ALLOY FOR HIGH TEMPERATURE USE OF THE TYPENORMALLY CONTAINING BORON, CHROMIUM MOLYBDENUM AND IRON, THE METHOD OFIMPAIRING HOT WORKABILITY AND COLD FORMABILITY PROPERTIES, WHICHCOMPRISES INCORPORATING TITANIUM AND ALUMINUM IN SAID ALLOY, REGULATINGTHE RATIO OF SAID TITANIUM TO SAID ALUMINUM BETWEEN 1.0 TO 1 AND 1.5 TO1, EXCLUDING THE EMBODIMENT OF BORON THEREIN WHILE RESTRICTING THE ALLOYCOMPOSITION TO 14% TO 17% CHROMIUM, 8% TO 12% IRON 4% TO 7% MOLYBDENUM,2,25% TO 5.0% TITANIUM, 1.75% TO 2.50% ALUMINUM, 0.08% TO 0.25% CARBON,REMINDER NICKLE AND INCIDENTAL IMPURITIES.